GNAT and SIGTERM (Linux x86_64)

[Bryan <brobinson.eng@gmail.com>]

I'm trying to capture SIGTERM in a very simple test program but I'm
running into some issues. When I execute the code (at the end of
message), I get the following output in my terminal when I send "kill -
SIGTERM <PID>:

> ./entry_point
SIGTERM handler is NOT reserved
!!! SIGTERM handler is NOT attached !!!
Terminated

I attached the signal handler in signals.ads, but it seems the handler
is still not attached.  The sample program in the Big Book of Ada
Programming for Linux attaches the handler in the package
specification, and I tried to follow the sample program.  To make
things more interesting, If I run this same code on a Mac OS X with
GNAT, I get the following as my output:

> ./entry_point
SIGTERM handler is reserved

raised PROGRAM_ERROR : Interrupt 15 is reserved

This happens even with the Unreserve_All_Interrupts in signals.ads.
The behavior of both the Linux and the Mac binary are leading me to--
perhaps wrongly--consider that there is something I am missing with
GNAT to allow it to work with UNIX signals.

Questions:
1) Do my pragma statements need to be in the specification or the
body?
2) Do I need to pass some sort of flag to gnat to enable signals?

I would greatly appreciate any input or advice on this issue.

--------------------------------------
Test program source code:
--------------------------------------
-- Signals.ads
with Ada.Interrupts; use Ada.Interrupts;
with Ada.Interrupts.Names; use Ada.Interrupts.Names;
package Signals is
  pragma Unreserve_All_Interrupts;
  protected type Signal_Handler is
    procedure Handle_SIGTERM;
    pragma Attach_Handler(Handle_SIGTERM, SIGTERM);
    pragma Interrupt_State (SIGTERM, System);
  end Signal_Handler;
end Signals;

-- Signals.adb
with Ada.Text_IO; use Ada.Text_IO;
package body Signals is
  protected body Signal_Handler is
    procedure Handle_SIGTERM is
    begin
      Put_Line( "SIGTERM caught!" );
    end Handle_SIGTERM;
  end Signal_Handler;
end Signals;

-- Entrypoint.adb
with Ada.Text_IO; use Ada.Text_IO;
with Ada.Interrupts; use Ada.Interrupts;
with Ada.Interrupts.Names; use Ada.Interrupts.Names;
with Signals; use Signals;

procedure Entry_Point is
  Shutdown_Flag : Boolean := False;
begin
  if Is_Reserved(SIGTERM) then
    Put_Line("SIGTERM handler is reserved");
  else
    Put_Line("SIGTERM handler is NOT reserved");
  end if;

  if Is_Attached(SIGTERM) then
    Put_Line("SIGTERM handler is attached");
  else
    Put_Line("!!! SIGTERM handler is NOT attached !!!");
  end if;

  loop
    -- do nothing
    exit when Shutdown_Flag = True;
  end loop;
end Entry_Point;